In recent years, energy transmission using a magnetic field resonant method has attracted attention as a technique allowing non-contact transmission of electric energy. With the magnetic resonant method, it has been known that electric power can be transmitted even though a distance between an electric power transmission portion and an electric power reception portion is greater than in an electromagnetic induction method.
In the magnetic resonant method, however, there is an optimal distance, and if a distance is too short, transmission efficiency is lowered. Japanese Patent Laying-Open No. 2011-50140 (PTD 1) discloses a technique with which high transmission efficiency can be maintained even though a distance between a transmission side and a reception side of electric power decreases to establish a close coupling state in a case that electric power is transmitted and received in a non-contact manner with the use of the resonant method.
According to a non-contact electric power transmission device disclosed in this document, in such a configuration that AC power from an AC power supply is supplied to a resonant element so that magnetic field is generated in the resonant element and AC power is supplied to an electric power reception device which becomes a receiving counterpart as a result of resonance, an automatic matching device is provided between the AC power supply and the resonant element. The automatic matching device adjusts impedance of the resonant element in accordance with a coefficient of coupling with the electric power reception device which is a target of supply of AC power.